Nonaqueous electrolyte battery having large capacity and long cycle life

ABSTRACT

It is intended to provide a nonaqueous electrolyte battery that satisfies both of a large discharge capacity and a superior cycle life characteristic by developing a novel negative electrode material. A nonaqueous electrolyte battery uses a negative electrode active material that is a compound expressed by Formula (1): 
     
       
         A z MX y   (1) 
       
     
     where A is at least one element selected from the alkali metals, M is at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir, Pt, and Mg, X is at least one element selected from the group consisting of B, N, Al, Si, P, Ga, Ge, As, In, Sn, Sb, Pb, and Bi, 0≦z≦20, and 0.2≦y≦6.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nonaqueous electrolyte battery and,more specifically, to a nonaqueous electrolyte battery having animproved negative electrode active material.

2. Description of the Background

Nonaqueous electrolyte secondary batteries using, as a negativeelectrode active material, metallic lithium, a lithium alloy, a lithiumcompound, a carbon material, or the like are anticipated to become goodhigh energy density batteries and are now researched and developedextensively. So far, a wide variety of lithium ion batteries that useLiCoO₂, LiMn₂O₄, or the like as a positive electrode material and acarbon material capable of inserting and de-inserting lithium as anegative electrode active material have been put into practical use.

On the other hand, although secondary batteries using, as a negativeelectrode active material, metallic lithium, a lithium alloy, a lithiumcompound are anticipated to exhibit a large capacity, they have not beenput into practical use yet for the following main reasons. The use ofmetallic lithium is associated with problems that lithium deterioratesowing to reaction between a nonaqueous electrolyte liquid and metalliclithium and that desorption of the negative electrode active materialthat is caused by dendrite-like (bark-like) lithium produced byrepetition of charging and discharging causes internal short circuitingor shortens the cycle life. To solve these problems, studies have beenmade in which a lithium alloy or a lithium compound is used as anegative electrode. However, in particular, in the case of using analloy such as a lithium-aluminum alloy, although thecharging/discharging efficiency is increased by virtue of reduction inthe degree of reaction between the negative electrode active materialand the nonaqueous electrolyte liquid, improvement in cycle lifecharacteristic is insufficient because repetition of deep charging anddischarging causes pulverization of the electrode.

From the viewpoint of increasing the negative electrode capacity, it hasbeen proposed to use a chalcogen compound such as an oxide as a negativeelectrode active material. For example, it has been proposed to improvethe cycle life characteristic by using SnO or SnO₂ (Japanese UnexaminedPatent Publication Numbers Hei. 7-122274 and Hei. 7-235293) or anamorphous oxide such as SnSiO₃ or SnSi_(1−x)P_(x)O₃. However, even theuse of those chalcogen compounds has not yet improved or increased thecycle life and the capacity sufficiently. A need, therefore, continuesto exist for a nonaqueous electrolyte battery which is not burdened bythese problems.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to provide a nonaqueouselectrolyte battery having a large capacity and a long cycle life byusing a negative electrode active material that has a large capacity andis superior in charging/discharging cycle performance.

The invention provides a nonaqueous electrolyte battery comprising apositive electrode, a negative electrode having a negative electrodeactive material that inserts and de-inserts an alkali metal, and anonaqueous electrolyte. The negative electrode active material is acompound that is expressed by Formula (1):

A _(z)MX_(y)  (1)

where A is at least one element selected from the alkali metals, M is atleast one element selected from the group consisting of Ti, V, Cr, Mn,Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir, Pt, and Mg, X is at least oneelement selected from the group consisting of B, N, Al, Si, P, Ga, Ge,As, In, Sn, Sb, Pb, and Bi, 0≦z≦20, and 0.2≦y≦6.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of an example of a nonaqueouselectrolyte battery (cylindrical nonaqueous electrolyte secondarybattery) according to the present invention; and

FIG. 2 is a partial sectional view of an example of a nonaqueouselectrolyte battery (coin-type battery) according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

By using, as a negative electrode active material, the compoundexpressed by Formula (1), a large amount of alkali metal such as Li isinserted, the reversibility of the insertion/de-insertion reaction isincreased, and the pulverization problem that is associated with acharging/discharging cycle is solved, whereby a battery having a longlife and a large capacity can be obtained. This is because by virtue ofthe presence of M atoms the compound that is expressed by Formula (1) iskept stable in structure even if it inserts an alkali metal and hencecrystal pulverization due to structural variation is inhibited.

In particular, from the viewpoint of increasing the capacity and batterylife, it is desirable that M be at least one element selected from thegroup consisting of Co, Fe, Ni, Cu, and Cr, and that X be at least oneelement selected from the group consisting of Al, P, As, Sb, and Bi.

From the viewpoint of increasing the capacity and the life, it isdesirable that X include Sb as a main component.

From the viewpoint of increasing the life, it is desirable that thecompound expressed by Formula (1) have at least one structure selectedfrom the group consisting of an NiAs structure, a FeS₂ structure, and aCoAs₃ structure. Where the compound has any of these structures, inparticular the volume expansion when it inserts an alkali metal issuppressed and hence crystal pulverization is inhibited.

It is desirable that the compound expressed by Formula (1) have anaverage crystal particle diameter that is greater than or equal to 1 nmand less than or equal to a value given by Formula (2):

3.0/{(V ₁ −V ₀)/V ₀}²[nm]  (2)

where V₀ and V₁ are volumes of the compound before and after charging,respectively.

By controlling the crystal particle diameter in the above range, thevolume variation due to insertion or de-insertion of an alkali metal isreduced and the life is thereby increased.

It is desirable that the compound expressed by Formula (1) have anaverage particle diameter in a range of 0.01-1.00 μm. By controlling thecrystal particle diameter in the above range, the volume variation dueto insertion or de-insertion of an alkali metal is reduced and the lifeis thereby increased.

It is preferable that the negative electrode include the compoundexpressed by Formula (1) and a nitride that is expressed by Formula (3):

A′_(a)M′_(b)N  (3)

where A′ is at least one element selected from the alkali metals, M′ isat least one element selected from the group consisting of Mn, Fe, Co,Ni, and Cu, 0<a≦3, and 0≦b≦1.

By adding the nitride that is expressed by Formula (3), the volumeexpansion due to occlusion of an alkali metal is reduced and the life isthereby increased. Further, the initial Coulomb efficiency is increased.

A nonaqueous electrolyte battery (e.g., a cylindrical nonaqueouselectrolyte secondary battery) according to the invention will bedescribed below in detail with reference to FIG. 1.

For example, an insulator 2 is provided at the bottom of a container 1that is made of stainless steel and assumes a cylinder having a bottom.An electrode group 3 is accommodated in the container 1. The electrodegroup 3 has a structure that a band-like member formed by stacking apositive electrode 4, a separator 5, a negative electrode 6 are wound ina spiral in such a manner that one of the separators 5 is locatedoutside.

An electrolyte is accommodated in the container 1. An insulating sheet 7having an opening at the center is disposed over the electrode group 3in the container 1. An insulating sealing plate 8 is disposed in a topopening of the container 1 and fixed to the container 1 by caulkinginward a portion of the container 1 that is adjacent to the top opening.A positive terminal 9 is fitted in a central hole of the insulatingsealing plate 8. One end of a positive electrode lead 10 is connected tothe positive electrode 4 and the other end is connected to the positiveterminal 9. The negative electrode 6 is connected to the container 1serving as a negative terminal via a negative electrode lead (notshown).

Next, the positive electrode 4, the separator 5, and the negativeterminal 6 will be described in detail.

1) Positive Electrode

For example, the positive electrode is manufactured by properlysuspending a positive electrode active material, a conductive material,and a binder in a solvent, applying a resulting suspension to acollector such as aluminum foil, drying the suspension, and pressing aresulting material into a band-like electrode.

The positive electrode active material is any of various kinds of oxidesand sulfides such as manganese dioxide (MnO₂), lithium manganesecomposite oxides (e.g., LiMn₂O₄ and LiMnO₂), lithium nickel compositeoxides (e.g., LiNiO₂), a lithium cobalt composite oxide (LiCoO₂),lithium nickel cobalt composite oxides (e.g., LiNi_(1−x)Co_(x)O₂),lithium manganese cobalt composite oxides (e.g., LiMn_(x)Co_(1−x)O₂),and vanadium oxides (e.g., V₂O₅). The positive electrode active materialmay also be any of various organic materials such as conductive polymermaterials and disulfide polymer materials. Even preferably, the positiveelectrode active material may be any of a lithium manganese compositeoxide (LiMn₂O₄), a lithium nickel composite oxide (LiNiO₂), a lithiumcobalt composite oxide, (LiCoO₂), a lithium nickel cobalt compositeoxide (LiNi_(0.8)Co_(0.2)O₂), lithium manganese cobalt composite oxides(LiMn_(x)Co_(1−x)O₂), and like materials all of which provide a highbattery voltage.

Examples of the conductive material are acetylene black, carbon black,and graphite.

Examples of the binder are polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), and fluoride rubbers.

It is preferable that the positive electrode active material, theconductive material, and the binder be blended at 80-95 wt. %, 3-20 wt.%, and 2-7 wt. %, respectively.

2) Separator

Example of the material of the separator are synthetic resin nonwovenfabric, polyethylene porous film, and polypropylene porous film.

3) Negative Electrode

For example, the negative electrode is manufactured by suspending anegative electrode active material, a conductive material, and a binderin a proper solvent, applying a resulting suspension to metal foil suchas copper foil, drying the suspension, and pressing a resulting materialinto a band-like electrode that is composed of the negative electrodeactive material, the conductive material, and the binder.

The negative electrode active material should contain at least acompound that is expressed by Formula (1):

A_(z)MX_(y)  (1)

where A is at least one element selected from the alkali metals, M is atleast one element selected from the group consisting of Ti, V, Cr, Mn,Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir, Pt, and Mg, X is at least oneelement selected from the group consisting of B, N, Al, Si, P, Ga, Ge,As, In, Sn, Sb, Pb, and Bi, 0≦z≦20, and 0.2≦y≦6.

In Formula (1), Li is desirable as the element A because Li provides ahigh energy density. From the viewpoint of increasing the capacity andthe life, it is desirable that M be at least one element selected fromthe group consisting of Co, Fe, Ni, Cu, and Cr, and that X be at leastone element selected from the group consisting of Al, P, As, Sb, and Bi.In particular, it is desirable that X include Sb as a main component.

A combination that M is at least one element selected from the groupconsisting of Ni, Co and Fe and X is Sb is particularly preferablebecause it provides a particularly long life and large capacity. As forthe element M, the order of desirability is Ni (most desirable), Co, andFe.

In Formula (1), parameters z and y should satisfy 0≦z≦20 and 0.2≦y≦6. Inparticular, from the viewpoint of increasing battery life, it isdesirable that z be in a range of 0.01≦z≦10. From the viewpoint ofincreasing the capacity and the life, it is desirable that y be in arange of 0.2≦y≦3.2. It is more desirable that y be in a range of0.8≦y≦3.2.

Among the alkali-metal-containing compounds expressed by Formula (1),particularly desirable compounds are Li_(z)Ni_(x)Fe_(1−x)Sb_(y),Li_(z)Ni_(x)Fe_(1−x−w)Co_(w)Sb_(y), Li_(z)Co_(x)Ni_(1−x)Sb_(y),Li_(z)Co_(x)Fe_(1−x)Sb_(y), Li_(z)CoBi_(1-v)Sb_(v), Li_(z)CoSi_(y), andLi_(z)CoAl_(y), where 0≦z≦20, 0.2≦y≦6, 0≦x≦1, 0.2≦v≦1, x+w≦1 and 0≦w≦1.

More specifically, among the alkali-metal-containing compounds expressedby Formula (1), Li_(z)Ni_(x)Fe_(1−x)Sb₃,Li_(z)Ni_(x)Fe_(1−x−w)Co_(w)Sb₃, Li_(z)Co_(x)Ni_(1−x)Sb₃,Li_(z)Co_(x)Fe_(1−x)Sb₃, Li_(z)Ni_(x)Fe_(1−x)Sb₂,Li_(z)Ni_(x)Fe_(1−x−w)Co_(w)Sb₂, Li_(z)Co_(x), Ni_(1−x)Sb₂, andLi_(z)Co_(x)Fe_(1−x)Sb₂ are desirable, where 0≦z≦20, 0≦x≦1, and 0≦w≦1.

Specifically, among the compounds expressed by Formula (1) that containno alkali metal, NiSb₂ is most desirable. CoSb₂ (most desirable), FeSb₂,Fe_(0.5)Ni_(0.5)Sb₃, and CoSb₃ are also desirable in this order.

It is desirable that the compound expressed by Formula (1) have astructure selected from the group consisting of an NiAs structure, aFeS₂ structure, and a CoAs₃ structure. Where the compound has any ofthese structures, in particular the volume expansion due to occlusion ofan alkali metal is suppressed and hence crystal pulverization isinhibited.

Where the battery is a nonaqueous secondary battery and a compound(e.g., LiCoO₂, LiMnO₂, or LiNiO₂) originally containing an alkali metalA (e.g., Li) is used in the positive electrode, if an MX_(y) compound(z=0) is used as the negative electrode active material, the alkalimetal A (e.g., Li) moves from the positive electrode to the negativeelectrode when the battery is charged for the first time and the MX_(y)compound turns to an A_(z)MX_(y) compound (Li_(z)MX_(Y)). That is, theMX_(y) compound serves as the negative electrode of the secondarybattery in such a manner as to insert and de-insert the alkali metal ina reversible manner. Even in a case where a compound containing analkali metal A is used in the positive electrode to stabilize acharging/discharging cycle, it is desirable that a compound containingan alkali metal A so as to satisfy 0<z≦20 be used as the negativeelectrode active material. Where a compound originally containing noalkali metal A (e.g., CoO₂, MnO₂, or NiO₂) is used as the positiveelectrode active material, a compound A_(z)MX_(y) (e.g., Li_(z)MX_(y);0≦z≦20 and 0.8≦y≦6) that originally contains an alkali metal or that isproduced electrochemically, for example, by laminating an alkali metaland an MX_(y) compound (z=0) may be used as the negative electrodeactive material.

Where the battery is a nonaqueous electrolyte primary battery, it isdesirable that a compound originally containing no alkali metal be usedin the positive electrode and a compound expressed by Formula (1) andcontaining an alkali metal so as to satisfy 0<z≦20 be used in thenegative electrode.

It is desirable that the negative electrode active material have anaverage crystal particle diameter that is greater than or equal to 1 nmand less than or equal to a value given by Formula (2):

3.0/{(V ₁ −V ₀)/V ₀}²[nm]  (2)

where V₀ and V₁ are volumes of the compound before and after charging,respectively.

By controlling the crystal particle diameter in the above range, thevolume variation due to insert or de-insert of an alkali metal isreduced and the life is thereby increased.

The pulverization that was conventionally problematic in alloy negativeelectrodes etc. is such that when insertion and de-insertion reactionsare repeated while a large amount of alkali metal such as Li isinserted, cracks develop in particles as the volume varies and theelectricity collecting efficiency lowers to a large extent. Thepulverization problem does not occur if cracks do not develop when suchvolume variation is repeated. Through thermodynamic stress analysis, theinventors have found that the development of cracks can be inhibited byproperly controlling the crystal particle diameter. The control methodwill be described below.

The energy of particles can be expressed by Equation (10):

U _(total) =U ₀ −U _(strain) +U _(surface)  (10)

where U_(total) is the total energy, U₀ is the internal energy of theparticles, U_(Strain) is the strain energy inside the particles, andU_(surface) is the surface energy of the particles.

If the shape of the particles is approximated by a dodecahedron,Equation (10) can be modified into Equation (11):

U _(total) =U ₀−7.66NU _(strain)+20.65Nγd ²  (11)

where N is the number of particles, γ is the surface energy of eachparticle, and d is the particle diameter.

Therefore, the destruction limit particle diameter d_(critical) is givenby Equation (12) and cracks do not develop in the particles if theparticle diameter is smaller than d_(critical):

d _(critical)=1.80γ/U _(strain).  (12)

Since U_(strain)=σ²/2E and σ={E/3(1−2ν)}{(V₁−V₀)/V₀}, Equation (12) isfinally modified into Equation (13):

d _(critical)=32.4γ(1−2ν)² /[E{(V ₁ −V ₀)/V ₀}²][m]  (13)

Therefore, the particle diameter is controlled so as to be smaller thand_(critical) that is given by Equation (13), the pulverization isinhibited and the life of the active material can be increased.

Equation (2) is obtained by substituting physical property values of acommon compound into Equation (13).

It is desirable that the negative electrode active material have anaverage particle diameter in a range of 0.01-100 μm. If the averageparticle diameter is smaller than 0.01 μm, it is difficult to uniformlydisperse the negative electrode active material over the electrodesurface. If the average particle diameter is larger than 100 μm, theelectrode surface is roughened, which is a factor of causingshort-circuiting and shortening of battery life.

Where the negative electrode active material contains no alkali metal A,it is manufactured by mixing powders of M and X at a prescribedstoichiometric ratio and heat-treating the powders at 400-1,000° C.,preferably at 400-800° C., in an inert gas atmosphere, a reducingatmosphere, or in a vacuum. In a heat treatment at a temperature lowerthan 400° C., it takes long time to form a compound through reaction;the productivity is low in this case. At a temperature higher than1,000° C., evaporation dissipation of X atoms having a high vaporpressure is remarkable and the composition varies to a large extent fromthe state at the time of the mixing of the powders.

Where the negative electrode active material contains an alkali metal A,it is manufactured by mixing powders of A_(z)X, M, and X at a prescribedstoichiometric ratio and heat-treating the powders at 400-1,000° C.,preferably at 400-800° C., in an inert gas atmosphere, a reducingatmosphere, or in a vacuum.

The negative electrode active material can be manufactured by othermethods. For example, it can be synthesized by using an arc dissolutionmethod, a high-frequency dissolution method, or the like. Grinding maybe performed by using a ball mill, a vibration mill, a planetary ballmill, a jet mill, or the like. A liquid-phase rapid cooling method, amechanical alloy method, a plating method, an evaporation method, asputtering method, a CVD method, or the like may be used, and any ofthese methods may be combined with a heat treatment.

It is preferable that the negative electrode of the nonaqueouselectrolyte battery include the compound expressed by Formula (1) and anitride that is expressed by Formula (3):

A′_(a)M′_(b)N  (3)

where A′ is at least one element selected from the alkali metals, M′ isat least one element selected from the group consisting of Mn, Fe, Co,Ni, and Cu, 0<a≦3, and 0≦b≦1.

By adding the nitride that is expressed by Formula (3), the nitride ofFormula (3) reduces the volume variation that occurs in the compound ofFormula (1) during charging and discharging and the life of the negativeelectrode is thereby increased. Further, since the addition of thenitride of Formula (3) allows an alkali metal to exist in the negativeelectrode in a stable manner, the initial Coulomb efficiency of thecompound of Formula (1) can greatly be increased.

As for the material that is expressed by Formula (3), if parameter b istoo small, the conductivity becomes low to cause fear that the batterycharacteristics may deteriorate. If parameter b is too large, transitionmetals are hard to form a solid solution. Therefore, parameter b shouldbe in a range of 0.1≦b≦0.8. To increase the stability of the crystalstructure and provide a superior cycle life characteristic, it ispreferable that parameter a be in a range of 1.5≦a≦3.

Although no particular limitations are imposed on the manufacturingmethod of the material that is expressed by Formula (3), it can bemanufactured by a solid-phase reaction method, for example. It ismanufactured by mixing an Li₃N powder and transition method elementpowders (starting materials) at a prescribed ratio that conforms to thecomposition of a target material and then heat-treating a resultingmixture in a high-purity nitrogen atmosphere. Heat treatment conditionsof 400-800° C. and about 1-100 hours are proper.

As for the combination of the materials of Formulae (1) and (3), toequalize potential flat portions, it is preferable that the material ofFormula (1) include Sb as an essential component and the material ofFormula (3) include Co and Cu as essential components. The mixing ratioof the materials of Formulae (1) and (3) can be determined properlydepending on the initial Coulomb efficiency values and the alkali metalcontents of the respective materials. However, from the viewpoint of thevolume energy density, it is preferable that the material of Formula (3)be added at 0.1-30 wt. %.

Examples of the conductive material are acetylene black, carbon black,and graphite.

Examples of the binder are polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), fluoride rubbers, ethylene-butadienerubber (SBR), and carboxymethylcellulose (CMC).

It is preferable that the negative electrode active material, theconductive material, and the binder be blended at 70-95 wt. %, 0-25 wt.%, and 2-10 wt. %, respectively.

4) Nonaqueous Electrolyte

Examples of the nonaqueous electrolyte are liquid electrolytes preparedby dissolving an electrolyte in a nonaqueous solvent, polymer gel-likeelectrolytes in which the above nonaqueous solvent and electrolyte arecontained in a polymer material, polymer solid electrolytes in whichonly the above electrolyte is contained in a polymer material, andinorganic solid electrolytes exhibiting lithium ion conductivity.

Known nonaqueous solvents in which a lithium salt as an electrolyte isdissolved in a nonaqueous solvent of a lithium battery can be used asthe liquid electrolyte. It is preferable to use a nonaqueous solventthat is mainly made of a cyclic carbonate such as ethylene carbonate(EC) or propylene carbonate (PC) or a mixed solvent of a cycliccarbonate and a nonaqueous solvent (hereinafter referred to as “secondsolvent”) that is lower in viscosity than the cyclic carbonate.

Examples of the second solvent are cyclic carbonates such as dimethylcarbonate, methylethyl carbonate, and diethyl carbonate,γ-butyrolactone, acetonitrile, methyl propionate, ethyl propionate,cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, andchain ethers such as dimethoxymethane and diethoxyethane.

Examples of the electrolyte are alkali salts, in particular, lithiumsalts. Examples of the lithium salt are lithium phosphate hexafluoride(LiPF₆), lithium borofluoride (LiBF₄), lithium arsenic hexafluoride(LiAsF₆), lithium perchlorate (LiClO₄), and lithiumtrifluorometasulfonate (LiCF₃SO₃). In particular, lithium phosphatehexafluoride (LiPF₆) and lithium borofluoride (LiBF₄) are preferable. Itis preferable that the dissolution amount of the electrolyte withrespect to the amount of the nonaqueous solvent be 0.5-2.0 mol/l.

The gel-like electrolyte is produced by dissolving the above solvent andelectrolyte in a polymer material so as to establish a gel-like state.Examples of the polymer material are such polymers of a monomer aspolyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), andpolyethylene oxide (PEO) and copolymers with another monomer.

The solid electrolyte is produced by dissolving the above electrolyte ina polymer material and solidifying a resulting solution. Examples of thepolymer material are such polymers of a monomer as polyacrylonitrile,polyvinylidene fluoride (PVdF), and polyethylene oxide (PEO) andcopolymers with another monomer. Examples of the inorganic solidelectrolyte are ceramic materials containing lithium. Among thoseceramic materials are Li₃N and Li₃PO₄—Li₂S—SiS₂ glass.

Although the cylindrical nonaqueous electrolyte secondary batteryaccording to the invention was described above with reference to FIG. 1,the invention can similarly be applied to batteries of other shapes suchas rectangular nonaqueous electrolyte batteries and button-typenonaqueous electrolyte batteries. The electrode group that isaccommodated in the container of the battery is not limited to oneshaving a spiral shape; positive electrodes, separators, and negativeelectrodes may be stacked in this order.

Having now generally described this invention, a further understandingcan be obtained by reference to certain specific examples which areprovided herein for purposes of illustration only and are not intendedto be limiting unless otherwise specified.

Details of the present invention will be described below with referenceto embodiments illustrated in the drawings.

Embodiment 1 to Embodiment 58 Manufacture of Positive Electrode

A positive electrode having an electrode density of 3.0 g/cm³ wasmanufactured by mixing together a lithium cobalt oxide (LiCoO₂; positiveelectrode active material) powder of 91 wt. %, acetylene black of 2.5wt. %, graphite of 3 wt. %, and polyvinylidene fluoride (PVdF) of 4 wt.%with addition of an N-methylpyrrolydone (NMP) solution, applying aresulting mixture to a collector of 15-μm thick aluminum foil, anddrying and pressing the mixture.

Manufacture of Negative Electrode

Manufacture of Negative Electrode in Embodiment 1

A Co powder having purity of 99% and an average particle diameter of 20μm and a Sb powder having purity of 99.9% and an average particlediameter of 20 μm were mixed with each other at an atomic equivalentratio of 1:3 and then stirred sufficiently with a V mixer. A resultingmixed powder was put in an alumina crucible and was caused to react witheach other by heat-treating those at 600° C. for 24 hours in an argongas flow. An XRD analysis on a heat-treated substance showed only onepeak of a CoSb₃ phase having a skutterudite structure, which indicatedthat this substance has a CoSb₃ structure. The reaction product thatcohered as a result of the reaction was ground into a CoSb₃ powderhaving an average particle diameter of 20 μm by using an agate mortar.

A negative electrode was produced by mixing together this CoSb₃ powderof 85 wt. %, graphite 5 wt. %, acetylene black 3 wt. %, and PVdF 7 wt. %with addition of an NMP solution, applying a resulting mixture to acollector of 12-μm thick copper foil, and drying and pressing themixture.

Manufacture of Negative Electrode in Embodiment 2

A CoO_(0.5)Ni_(0.25)Fe_(0.25)Sb₃ powder having an average particlediameter of 20 μm was obtained by mixing together a 325-mesh Co powder(average particle diameter: 20 μm), a 325-mesh Ni powder (averageparticle diameter: 20 μm), a 325-mesh Fe powder (average particlediameter: 20 μm), and a 325-mesh Sb powder (average particle diameter:20 μm) at a prescribed mol ratio and heat-treating a resulting mixtureat 600° C. for 24 hours in an argon atmosphere.

A negative electrode was produced by mixing together thisCo_(0.5)Ni_(0.25)Fe_(0.25)Sb₃ powder of 85 wt. %, graphite 5 wt. %,acetylene black 3 wt. %, and PVdF of 7 wt. % with addition of an NMPsolution, applying a resulting mixture to a collector of 12-μm thickcopper foil, and drying and pressing the mixture.

Manufacture of Negative Electrode in Embodiment 44

An Mn powder having purity of 99% and an average particle diameter of 20μm and an Sb powder having purity of 99.9% and an average particlediameter of 20 μm were mixed with each other at an atomic equivalentratio of 2:1 and then stirred sufficiently with a V mixer. A resultingmixed powder was put in an alumina crucible and was caused to react witheach other by heat-treating those at 600° C. for 120 hours in an argongas flow. An XRD analysis on a heat-treated substance showed only onepeak of an Mn₂Sb phase having a Cu₂Sb structure, which indicated thatthis substance is of an Mn₂Sb single phase. The reaction product thatcohered as a result of the reaction was ground into an Mn₂Sb powderhaving an average particle diameter of 20 μm by using an agate mortar.

A negative electrode was produced by mixing together this Mn₂Sb powderof 85 wt. %, graphite 5 wt. %, acetylene black 3 wt. %, and PVdF of 7wt. % with addition of an NMP solution, applying a resulting mixture toa collector of 12-μm thick copper foil, and drying and pressing themixture.

Manufacture of Electrode Group

An electrode group was manufactured by stacking the above-describedpositive electrode, a separator made of polyethylene porous film, theabove-described negative electrode, and the same separator in this orderand winding a resulting stacked member in a spiral so that the negativeelectrode becomes the outermost layer.

Preparation of Nonaqueous Electrolyte Liquid

A nonaqueous electrolyte liquid was prepared by dissolving lithiumphosphate hexafluoride (LiPF₆) in a mixed solvent (volume mixing ratio:1:2) of ethylene carbonate (EC) and methylethyl carbonate (MEC) at 1.0mol/l.

Two kinds of cylindrical nonaqueous electrolyte secondary batteriesaccording to Embodiments 1 and 2 were assembled as shown in FIG. 1 byaccommodating the above electrode group and the electrolyte in acylindrical stainless steel container having a bottom.

Nonaqueous electrolyte secondary batteries according to Embodiments3-43, Embodiments 44-58, and Comparative Examples 1-9 were assembledthat were the same as the nonaqueous electrolyte secondary battery ofEmbodiment 1 except that negative electrode materials shown in Tables 1,2, and 3 are used, respectively.

For the thus-obtained batteries of Embodiments 1-43, Embodiments 44-58,and Comparative Examples 1-9, constant voltage charging (0.5 C, 4 V) wasperformed for 3 hours and then the capacity was measured after 0.5-Cdischarging (final discharge voltage: 2.4 V). The number of cycles afterwhich the capacity decreased to 80% of the value at the first cycle wasemployed as the cycle life. Results are summarized in Tables 1-3.

TABLE 1 Discharge Embodiment Negative electrode capacity Cycle numberactive material (mAh) life (cycles) Embodiment 1 CoSb₃ 2000 250Embodiment 2 Co_(0.5)Ni_(0.25)Fe_(0.25)Sb₃ 2000 300 Embodiment 3 RhSb₃2000 250 Embodiment 4 IrSb₃ 1900 200 Embodiment 5 CoP₃ 1700 250Embodiment 6 RhP₃ 1750 200 Embodiment 7 IrP₃ 1800 200 Embodiment 8 CoAs₃1800 250 Embodiment 9 RhAs₃ 1800 250 Embodiment 10 IrAs₃ 1850 200Embodiment 11 Fe_(0.1)Co_(0.8)Ni_(0.1)Sb₃ 2100 300 Embodiment 12Fe_(0.25)Co_(0.5)Ni_(0.25)Sb₃ 2200 350 Embodiment 13 Fe_(0.5)Ni_(0.5)Sb₃2050 300 Embodiment 14 Fe_(0.5)Ni_(0.5)As₃ 1900 400 Embodiment 15CoSi_(1.5)S_(1.5) 1700 350 Embodiment 16 CoSn_(1.5)S_(1.5) 1750 300Embodiment 17 CoSn_(1.5)Se_(1.5) 1750 300 Embodiment 18RhSn_(1.5)S_(1.5) 1800 250 Embodiment 19 IrSn_(1.5)S_(1.5) 1800 250Embodiment 20 Li_(0.001)Co_(0.5)Ni_(0.25)Fe_(0.25)Sb₃ 2200 700Embodiment 21 Li_(0.001)CoSb₃ 2000 300 Embodiment 22Li_(0.001)Fe_(0.5)Ni_(0.5)Sb₃ 2000 350 Embodiment 23Li_(0.01)Fe_(0.5)Ni_(0.5)Sb₃ 2100 400 Embodiment 24Li_(0.5)Ni_(0.5)Fe_(0.5)Sb₃ 2100 400 Embodiment 25Ni_(0.5)Fe_(0.25)Cu_(0.25)Sb₃ 2000 400 Embodiment 26 CoSb 1500 250Embodiment 27 Li_(0.1)CoSb 2100 350 Embodiment 28 LiCoSb₃ 2200 400

TABLE 2 Discharge Embodiment Negative electrode capacity number activematerial (mAh) Cycle life (cycles) Embodiment 29 CoAlSb₂ 1800 500Embodiment 30 CoPbSb₂ 1600 400 Embodiment 31 CoBiSb₂ 2000 600 Embodiment32 CoBSb₂ 1700 400 Embodiment 33 CoSi_(0.5)P_(0.5)Sb₂ 2500 300Embodiment 34 CoIn_(0.5)Sn_(0.5)Sb₂ 2400 300 Embodiment 35CoAs_(0.5)Ga_(0.5)Sb₂ 2000 400 Embodiment 36 Ni_(0.5)Mn_(0.5)Sb₃ 1800400 Embodiment 37 Fe_(0.75)V_(0.25)Sb₃ 1900 300 Embodiment 38Ni_(0.5)Ir_(0.5)Sb₃ 1700 300 Embodiment 39 Fe_(0.5)Ti_(0.5)Sb₃ 1500 400Embodiment 40 CoSb₂ 2000 500 Embodiment 41 NiSb₂ 2400 600 Embodiment 42FeSb₂ 1800 400 Embodiment 43 CrSb₂ 1900 400

TABLE 3 Discharge Embodiment Negative electrode capacity number activematerial (mAh) Cycle life (cycles) Embodiment 44 Mn₂Sb 1200 500Embodiment 45 Cu₂Sb 1000 480 Embodiment 46 Cu₃Sb 850 550 Embodiment 47Ni₃Sb 900 530 Embodiment 48 Ni₅Sb₂ 1000 480 Embodiment 49 Ni₇Sb₃ 1100450 Embodiment 50 Ni₂MnSb 850 530 Embodiment 51 Co₂MnSb 700 570Embodiment 52 FeVSb 1000 500 Embodiment 53 CoTiSn 1200 480 Embodiment 54NiTiSb 1000 520 Embodiment 55 CoNbSb 900 500 Embodiment 56 CoVSb 1000500 Embodiment 57 LiMn₂Sb 1300 550 Embodiment 58 Li_(0.01)Cu₂Sb 1050 520Comparative Al 1000 150 Example 1 Comparative Sn 1300 100 Example 2Comparative SnO 780 50 Example 3 Comparative SnO₂ 700 80 Example 4Comparative Sb 1200 120 Example 5 Comparative Bi 1200 150 Example 6Comparative Li 1400 80 Example 7 Comparative Li—Al Alloy 1200 120Example 8 Comparative C 300 1000 Example 9

It is seen from the above results that the negative electrode activematerials according to the invention provide nonaqueous electrolytesecondary batteries having large capacities and superiorcharging/discharging cycle characteristics.

EMBODIMENT 59

Batteries were manufactured by using, as negative electrode activematerials, Ni₂MgSb powders having average crystal particle diameters of10 μm (A), 1 μm (B), 100 nm (C), 10 nm (D), and 5 nm (E). Constantvoltage charging (0.5 C, 4 V) was performed for 3 hours and then thecapacity was measured after 0.5-C discharging (final discharge voltage:2.4 V). The number of cycles after which the capacity decreased to 80%of the value at the first cycle was employed as the cycle life. Thecycle life was represented by c, b, a, and aa when the number of cycleswas less than 100, 100-299, 300-499, 500 or more, respectively. Resultsare summarized in Table 4.

TABLE 4 Ni₂MnSb sample (A) (B) (C) (D) (E) Cycle life c b a aa aa

For the Ni₂MnSb negative electrodes of (A)-(E), lattice constantvariations between states before and after charging were measured byX-ray diffraction and volume variations of the unit lattice (V₀: volumebefore charging, V₁: volume after charging) were calculated. Values of(V₁−V₀)/V₀ were about 0.06. If this value is substituted into Formula(2), a value 0.83 μm is obtained. This result supports the finding ofthe invention that the cycle life characteristic is improved if theaverage crystal particle diameter is smaller than this value.

EMBODIMENT 60

CuMgSb powders having average crystal particle diameters of 100 μm (F),10 μm (G), 1 μm (H), 100 nm (I), and 10 nm (J) were synthesized andbatteries were manufactured in the same manner as in Embodiment 59. Themanufactured batteries were subjected to a cycle test under the sameconditions as in Embodiment 59. Results are summarized in Table 5.

TABLE 5 CuMgSb sample (F) (G) (H) (I) (J) Cycle life c b a aa aa

For the CuMgSb negative electrodes of (F)-(J), lattice constantvariations between states before and after charging were measured byX-ray diffraction and volume variations of the unit lattice (V₀: volumebefore charging, V₁: volume after charging) were calculated. Values of(V₁−V₀)/V₀ were about 0.048. If this value is substituted into Formula(2), a value 1.3 μm is obtained. This result supports the finding of theinvention that the cycle life characteristic is improved if the averagecrystal particle diameter is smaller than this value.

EMBODIMENT 61 Manufacture of Negative Electrode

A Co powder having purity of 99% and an average particle diameter of 20μm and an Sb powder having purity of 99.9% and an average particlediameter of 20 μm were mixed with each other at an atomic equivalentratio of 2:1 and then stirred sufficiently with a V mixer. A resultingmixed powder was put in an alumina crucible and was caused to react witheach other by heat-treating those at 600° C. for 120 hours in an argongas flow. An XRD analysis on a heat-treated substance showed only onepeak of a CoSb₃ phase having a CoAs₃ structure, which indicated thatthis substance is of a CoSb₃ single phase. The reaction product thatcohered as a result of the reaction was ground into a CoSb₃ powderhaving an average particle diameter of 20 μm by using an agate mortar.

Then, an Li₃N powder having purity of 99% and an average particlediameter of 20 μm and a Co powder having purity of 99% and an averageparticle diameter of 20 μm were mixed with each other with an Li-to-Coatomic ratio of 2.6:0.4 and then stirred sufficiently. AnLi_(2.6)Co_(0.4)N powder was produced by putting a resulting mixedpowder in an agate crucible and firing it at 700° C. for 8 hours in ahigh-purity (99.9%) nitrogen atmosphere.

A negative electrode was produced by mixing together this CoSb₃-phasepowder of 72.3 wt. %, an Li_(2.6)Co_(0.4)N powder of 12.7 wt. %,graphite 5 wt. %, acetylene black 3 wt. %, and PVdF of 7 wt. % withaddition of an NMP solution, applying a resulting mixture to a collectorof 12-μm thick copper foil, and drying and pressing the mixture.

Negative electrodes in which the contents of the CoSb₃-phase powder andthe Li_(2.6)Co_(0.4)N powder were varied in ranges of 76.5-85 wt. % and0-8.5 wt. %, respectively, were manufactured in the same manner.

Manufacture of Battery

By using each of the above negative electrodes, a coin-type battery of20 mm in diameter and 1.6 mm in thickness shown in FIG. 2 wasmanufactured. In FIG. 2, reference numeral 21 denotes a battery case;22, a collector; 23, an electrode; 24, a separator; 25, a metal Lielectrode; 26, a sealing plate; and 27, a gasket. The collector 22 thatis a stainless steel expanded metal member is welded to the insidesurface of the battery case 21. The electrode 23 that is worked into a15-mm-diameter disc is press-attached to the collector 22 from above.After an electrolyte liquid is injected so as to fall onto the electrode23, the electrode 23 was covered with the polypropylene separator 24 andthe sealing plate 26 to which the disc-shaped metal Li electrode 25(counter electrode) is press-attached inside with the gasket interposedin between. A coin-type battery was completed by caulking an end portionof the case 21. The electrolyte liquid was a nonaqueous electrolytesolution prepared by dissolving lithium phosphate hexafluoride (LiPF₆)in a mixed solvent (volume mixing ratio: 1:2) of ethylene carbonate (EC)and methylethyl carbonate (MEC) at 1.0 mol/l.

Test Method

For the coin-type batteries manufactured in the above manner, constantcurrent (0.5 mA/cm²) charging and discharging (upper cut voltage: 2.0 V,lower cut voltage: 0.1 V). Since the batteries are so designed as to becharged with excess counter electrode metal Li for an expected electrodecapacity, basically the charging/discharging characteristic depends ononly the test electrode.

TABLE 6 Active material Initial Coulomb Discharge constituents andefficiency capacity sample contents (%) (mAh/g) A CoSb₃(80.8 wt. %)/ 87660 Li_(2.6)Co_(0.4)N(4.2 wt. %) B CoSb₃(76.5 wt. %)/ 91 680Li_(2.6)Co_(0.4)N(8.5 wt. %) C CoSb₃(72.3 wt. %)/ 96 700Li_(2.6)Co_(0.4)N(12.7 wt. %) Comparative CoSb₃(85 wt. %) 84 630 Example

EMBODIMENT 62

Batteries were manufactured and evaluated in the same manners as inEmbodiment 61 except that NiSb₂ and Li_(2.6)Cu_(0.4)N were used as theactive material.

TABLE 7 Active material Initial Coulomb Discharge constituents andefficiency capacity sample contents (%) (mAh/g) D NiSb₂(80.8 wt. %)/ 87590 Li_(2.6)Cu_(0.4)N(4.2 wt. %) E NiSb₂(76.5 wt. %)/ 90 610Li_(2.6)Cu_(0.4)N(8.5 wt. %) F NiSb₂(72.3 wt. %)/ 93 630Li_(2.6)Cu_(0.4)N(12.7 wt. %) G NiSb₂(68 wt. %)/ 96 650Li_(2.6)Cu_(0.4)N(17 wt. %) Comparative NiSb₃(85 wt. %) 84 570 Example

EMBODIMENT 63

Batteries were manufactured and evaluated in the same manners as inEmbodiment 61 except that Ni₂MnSb and Li_(2.6)Co_(0.4)N were used as theactive material.

TABLE 8 Active material Initial Coulomb Discharge constituents andefficiency capacity sample contents (%) (mAh/g) H NiS₂MnSb(80.8 wt. %)/72 250 Li_(2.6)Co_(0.4)N(4.2 wt. %) I NiS₂MnSb(76.5 wt. %)/ 84 300Li_(2.6)Co_(0.4)N(8.5 wt. %) J NiS₂MnSb(72.3 wt. %)/ 96 350Li_(2.6)Co_(0.4)N(12.7 wt. %) Comparative Ni₃Sb(85 wt. %) 60 200 Example

It is seen from the above results that the invention increases theinitial Coulomb efficiency of the lithium compound.

The disclosures of Japanese priority Application Nos. 11-225491 filedAug. 9, 1999 and 2000-95529 filed Mar. 30, 2000 are hereby incorporatedby reference into the application.

What is claimed as new and is intended to be secured by Letters Patentis:
 1. A nonaqueous electrolyte battery comprising: a positiveelectrode; a negative electrode having a negative electrode activematerial that inserts and de-inserts an alkali metal, the negativeelectrode active material being a compound that is expressed by Formula(1): A_(z)MX_(y)  (1)  where A is at least one element selected from diegroup consisting of the alkali metals, M is at least one elementselected from the group consisting of Co, Fe, Ni, Cu and Cr and X is atleast one element selected from the group consisting of Al, P, As, Sband Bi, 0≦z≦20, and 0.2≦y≦6; and nonaqueous electrolyte.
 2. Thenonaqueous electrolyte battery according to claim 1, wherein, in thecompound expressed by Formula (1), elemental component X comprises atleast one element of which Sb is a main component.
 3. The nonaqueouselectrolyte battery according to claim 1, wherein the compound expressedby Formula (1) has at least one structure selected from the groupconsisting of an NiAs structure, a FeS₂ structure, and a CoAs₃structure.
 4. The nonaqueous electrolyte battery according to claim 1,wherein in Formula (1) z is in a range of 0.01≦z≦10.
 5. The nonaqueouselectrolyte battery according to claim 1, wherein in Formula (1) y is ina range of 0.2≦y≦3.2.
 6. The nonaqueous electrolyte battery according toclaim 5, wherein in Formula (1) y is in a range of 0.8≦y≦3.2.
 7. Thenonaqueous electrolyte battery according to claim 1, wherein thenegative electrode active material has an average particle diameter in arange of 0.01-100 μm.
 8. The nonaqueous electrolyte battery according toclaim 1, wherein the negative electrode consists of the negativeelectrode active material, a conductive material, and a binder which isa material selected from the group consisting ofpolytetrafluoroethylene, polyvinylidene fluoride, fluoride rubbers,ethylene-butadiene rubber and carboxymethylcellulose.
 9. The nonaqueouselectrolyte battery according to claim 1, wherein the negative electrodeconsists of the negative electrode active material, a binder and aconductive material selected from the group consisting of acetyleneblack, carbon black and graphite.
 10. The nonaqueous electrolyte batteryaccording to claim 1, wherein the negative electrode consists of thenegative electrode active material, a conductive material, and a binderwhich are blended in amounts of 70-95 wt. %, 0-25 wt. %, and 2-10 wt. %,respectively.
 11. The nonaqueous electrolyte battery according to claim1, wherein the compound expressed by Formula (1) has an average crystalparticle diameter that is greater than or equal to 1 nm and less than orequal to a value given by Formula (2): 3.0/{(V ₁ −V ₀)/V ₀}²[nm]  (2)where V₀ and V₁ are volumes of the compound before and after charging,respectively.
 12. The nonaqueous electrolyte battery according to claim1, wherein the negative electrode includes the compound expressed byFormula (1) and a nitride that is expressed by Formula (3):A′_(a)M′_(b)N  (3) where A′ is at least one element selected from thegroup consisting of the alkali metals, M′ is at least one elementselected from the group consisting of Mn, Fe, Co, Ni, and Cu, 0<a≦3, and0≦b≦1.
 13. A nonaqueous electrolyte battery comprising: a positiveelectrode; a negative electrode having a negative electrode activematerial that inserts and de-inserts an alkali metal, the negativeelectrode active material being a compound selected from the groupconsisting of Li_(z)Ni_(x)Fe_(1−x)Sb_(y),Li_(z)Ni_(x)Fe_(1−x−w)Co_(w)Sb_(y), Li_(z)Co_(x)Ni_(1−x)Sb_(y),Li_(z)Co_(x)Fe_(1−x)Sb_(y), Li₂CoBi_(1−v)Sb_(v), Li_(z)CoSi_(y), andLi_(z)CoAl_(y), where 0≦z≦20, 0.2≦y≦6, 0≦x≦1, 0.2≦v≦1, x+w≦1, and 0≦w≦1;and a nonaqueous electrolyte.
 14. The nonaqueous electrolyte batteryaccording to claim 13, wherein the negative electrode active materialhas an average particle diameter in a range of 0.01-100 μm.
 15. Thenonaqueous electrolyte battery according to claim 13, wherein thenegative electrode consists of the negative electrode active material, aconductive material, and a binder which is a material selected from thegroup consisting of polytetrafluoroethylene, polyvinylidene fluoride,fluoride rubbers, ethylene-butadiene rubber and carboxymethylcellulose.16. The nonaqueous electrolyte battery according to claim 13, whereinthe negative electrode consists of the negative electrode activematerial, a conductive material which is selected from the groupconsisting of acetylene black, carbon black, and graphite and a binder.17. The nonaqueous electrolyte battery according to claim 13, whereinthe negative electrode consists of the negative electrode activematerial, a conductive material, and a binder which are blended inamounts of 70-95 wt. %, 0-25 wt. %, and 2-10 wt. %, respectively. 18.The nonaqueous electrolyte battery according to claim 13, wherein thecompound expressed by Formula (1) has an average crystal particlediameter that is greater than or equal to 1 nm and less than or equal toa value given by Formula (2): 3.0/{(V ₁ −V ₀)/V ₀}²[nm]  (2) where V₀and V₁ are volumes of the compound before and after charging,respectively.
 19. The nonaqueous electrolyte battery according to claim13, wherein the negative electrode further comprises a nitride that isexpressed by Formula (3): A′_(a)M′_(b)N  (3) where A′ is at least oneelement selected from the group consisting of the alkali metals, M′ isat least one element selected from the group consisting of Mn, Fe, Co,Ni, and Cu, 0<a≦3, and 0≦b≦1.